Our invention relates generally to cathode ray oscilloscopes (CROs) and pertains more specifically to a CRO of the class comprising a scan converter storage tube (hereinafter referred to simply as the storage tube) and a cathode ray tube (CRT).
The combination of a storage tube and a CRT together with associated control circuitry constitutes, per se, a known system, such that signal waveforms for observation or measurement can be introduced (written) into the storage tube for later extraction (reading) and display on the screen of the CRT.
Our Japanese Patent Application No. 54-117525, laid open to public inspection as 56-40763 on Apr. 17, 1981, represents an example of CRO with a built-in storage tube. In this prior art CRO the storage tube and CRT share a vertical and a horizontal amplifier. The parallel connection of the storage tube and CRT makes possible the use of the CRO in the following modes:
1. The direct display of the input waveform on the CRT screen, not via the storage tube, as is the case with ordinary CROs.
2. The indirect display of the input waveform on the CRT screen after its writing onto, and reading from, the storage tube.
3. The display of the input waveform on the CRT screen at the same time with its writing onto the storage tube.
In short the waveform being exhibited on the CRT screen may have either passed or bypassed the storage tube. We have found that our earlier CRO has a problem in connection with the display positions on the CRT screen of a waveform direct from the signal input of the instrument and that read from the storage tube. The CRT screen should give an exact replica of the input waveform in the same position thereon regardless of whether it is direct from the signal input or has been stored in the storage tube.
Our earlier CRO, however, displays one and the same waveform in horizontally displaced positions on the CRT screen depending upon whether it has passed or bypassed the storage tube, if the center-to-center distance between the pair of vertical deflection plates and pair of horizontal deflection plates of the CRT differs from the center-to-center distance between the pair of vertical deflection plates and pair of horizontal deflection plates of the storage tube, as will be later explained in further detail. Since some difference between these distances is customary, the above problem needs some practical solution.